Social Network Sites allow individuals to construct a public or semi-public profile within a bounded system, articulate a list of other users with whom they share a connection, and view and traverse their list of connections and those made by others within a system. Such sites are generally centered around a particular activity, such as maintaining social relationships or uploading user created content. Increasingly, niche domains such as education, healthcare and software development have been exploring the creation of social network sites centered around the activities of the domain. This has led to an increasing focus on the processes involved in designing and evaluating these sites. We argue that social network sites require a specialized focus in their design and evaluation on the social utility of the features on the site. We have created two social network sites for niche communities: Colloki, a conversation platform designed for members of local communities; and CATspace, a social repository of Computer Science assignments, designed for use by CS instructors and students. In this thesis, we describe the motivation, design and implementation of these two sites. We provide a formative evaluation of these two sites, wherein we evaluate the usability, and study the perceived social affordances of individual features across the two site. Finally, we discuss future work towards building a framework for evaluating the social utility of Social Network Sites at a formative stage.